Not getting 12 volts to coil

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Dusten

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71 Duster with 340. Electronic mopar ignition single ballast resistor. Engine tries to start but can't. More like sputters. Only getting 8 volts at + coil terminal when cranking/start. I found that I can get 12 volts to the + coil when I disconnect the wire connected to the negative coil terminal. The one that goes to the ecu. Also get 12 volts to the + coil if I disconnect or un ground the ecu unit. All readings when the engine is start/cranking. My problem is I don't know what these results mean? I have tried 2 different ecu boxes. My original chrome ecu box and a new hirev 7500 ecu. I also jumped the ballast. Same results. Thanks in advance for any advice.
 
Don't lead yourself down wrong paths. You are changing the circuit (wiring) and it is giving you FALSE results
The system will not work/ won't run with ECU ungrounded.
When you unhook the coil NEG of course the ballast shows 12---the ECU wire going to coil NEG causes the coil to draw current through the ballast resistor and that pulls the voltage down....just like it is supposed to

Measurements

Measure coil POS with key on/ engine stopped. (and everything connected normally) Should read somewhere 6--10V. If it reads 12 either the ballast is bypassed or the coil is not drawing current, meaning "some ting wong"

If that is OK, disconnect dist. pickup wire. Again with key "in run" take the dist. connector engine bay end, not the dist end, and repeatedly tap the bare connector pin onto ground. Use a test gap/ spark plug connected to coil tower. You should get one single "snap!" spark each time you ground it

Next, clip your meter to coil+ Crank engine USING THE KEY. You should get "same as battery" during cranking. In other words if battery reads 10.8V during cranking, then the coil+ should be about the same. If it is quite a bit lower or zero, the brown ballast bypass circuit is not working

If that is OK, check spark with test gap at coil tower crank and test using the key. If you get no spark, and the earlier test with the dist. connector did, then you may have a dist. pickup problem OR THE CONNECTOR may not be making contact which is common.

Inspect the inside of the dist. around the pickup / reluctor for rust/ debri, for strike damage, and check dist. shaft for wobble/ looseness. Work the dist connector in /out several times, to scrub the terminals clean, and to "feel" for tightness. Inspect the connector terminals with a lamp to check for corrosion. Same deal with the ECU connector ECU MUST BE GROUNDED
 
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If the 8 volts at the coil you mentioned in your post was found WHEN USING THE KEY to crank engine, you have a poor connection in the bypass circuit. This comes off a special, separate, dedicated contact on the ignition switch and is normally (but not always) brown. It's job is to supply ignition power straight to the coil+ when cranking.

IF YOU ARE TESTING by jumpering the starter relay, to crank, you are setting up ABNORMAL conditons, and your testing will be flawed.

When key is in "run" the system gets "ignition run" power from IGN1 on the ignition switch. This is the ONLY "run" switched power under the hood, and IS NOT fused. Normally blue, it comes from the ignition switch, through the bulkhead connector, and supples the VR IGN power terminal, the ballast, the alternator field (blue) and other accessories such as smog or electric choke

When key is in "start" that "run" IGN1 power GOES DEAD

The ONLY power for the system during cranking (using the key) comes from the ballast bypass, the brown IGN2. It only goes one place---from the IGN2 terminal on the ignition switch, out through the bulkhead, to the coil+ side of the ballast
 
Wow ! 67Dart273 is the man !! I’m not very good with electrical.... Sounds like 67Dart273 is very schooled in it !!!

One simple thing I would add ! I’ve had problem after problem with a bad distributor rotor ! Not sure why .. But I always carry one with me ! Atleast once a year I have to replace it for a no start condition...... How you can test to see if the rotor is bad.. Is pull the coil wire off the distributor.. Then take the distributor cap off... Hoid the coil wire about an 1/8 inch or so away from the top of the distributor rotor.. Now have someone turn the engine over... If fire jumps from the coil wire to the rotor.. The rotor is bad ! Replace your rotor..
 
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Wow ! 67Dart273 is the man !! I’m not very good with electrical.... Sounds like 67Dart273 is very schooled in it !!!

I had cranking issues for about 6 years until 67Dart273 saved my ***. Now my motor cranks awesome with a battery thats only at 75%. Don't want to buy a new one until spring. I've copied and pasted lots of his posts for futher down the road such as this post.:thumbsup:
 
Hello All.
Yes, We need more like "67Dart273"
As a wise man once said
"Just the facts, ma'am."
Stay Safe....
Happy Mopar :)
Arron
 
How you can test to see if the rotor is bad.. Is pull the coil wire off the distributor.. Then take the distributor cap off... Hoid the coil wire about an 1/8 inch or so away from the top of the distributor rotor.. Now have someone turn the engine over... If fire jumps from the coil wire to the rotor.. The rotor is bad ! Replace your rotor
Just a note... Rotor is bad because it is allowing current to find a ground path through the distributor
 
One simple thing I would add ! I’ve had problem after problem with a bad distributor rotor ! Not sure why .. But I always carry one with me ! Atleast once a year I have to replace it for a no start condition...... How you can test to see if the rotor is bad.. Is pull the coil wire off the distributor.. Then take the distributor cap off... Hoid the coil wire about an 1/8 inch or so away from the top of the distributor rotor.. Now have someone turn the engine over... If fire jumps from the coil wire to the rotor.. The rotor is bad ! Replace your rotor..

Actually you want to be careful with this test. The higher the output of your system, such as MSD, the more it can jump. Also, a WEAK spark that "seems to be" jumping in this test may simply be something similar to corona discharge. In other words you may be getting fooled.

If you are failing quite a few rotors, there is likely another reason.......such as something wrong in the distributor clearances, or bad plug wires, way too much plug gap, etc etc that is allowing spark voltage to run "high." Spark voltage is not like a 120V outlet. Spark voltage goes sky high when unloaded/ disconnected. So the "chain" of the output determines what that is. The coil wire, the rotor gap, the resistance/ condition of plug wires, whether plugs are resistor or internal gap, and the gap in the chamber, as well as engine load and AF ratio all determine spark voltage, as well as whatever the system puts out in power. Higher power---higher voltage.
 
Just a note... Rotor is bad because it is allowing current to find a ground path through the distributor

Yes. Rotors can "punch through" between the top and the shaft and carbon track right through the rotor material. This was (is?) a problem on OEM GM HEI as I mentioned.......bad plug wires, etc.
 
Actually you want to be careful with this test. The higher the output of your system, such as MSD, the more it can jump. Also, a WEAK spark that "seems to be" jumping in this test may simply be something similar to corona discharge. In other words you may be getting fooled.

If you are failing quite a few rotors, there is likely another reason.......such as something wrong in the distributor clearances, or bad plug wires, way too much plug gap, etc etc that is allowing spark voltage to run "high." Spark voltage is not like a 120V outlet. Spark voltage goes sky high when unloaded/ disconnected. So the "chain" of the output determines what that is. The coil wire, the rotor gap, the resistance/ condition of plug wires, whether plugs are resistor or internal gap, and the gap in the chamber, as well as engine load and AF ratio all determine spark voltage, as well as whatever the system puts out in power. Higher power---higher voltage.

As I said before I definitely am not an electrician !! My race car had all new ignition stuff ! All good stuff ! All I know is , if it wouldn’t crank I tested the rotor and it always jump fire to the rotor ! I put new rotor on and I was good tell the next racing season ! My son had a no start on his 1997 F250 460 that he messed with for days ! He calls me ! I tell him to check the rotor ! It jumped fire ! Once again he puts a new rotor on it’s been running ever since. ! I totally get what your saying tho ! But in my situation distributor rotors has been my huckleberry lol !!
 
Don't lead yourself down wrong paths. You are changing the circuit (wiring) and it is giving you FALSE results
The system will not work/ won't run with ECU ungrounded.
When you unhook the coil NEG of course the ballast shows 12---the ECU wire going to coil NEG causes the coil to draw current through the ballast resistor and that pulls the voltage down....just like it is supposed to

Measurements

Measure coil POS with key on/ engine stopped. (and everything connected normally) Should read somewhere 6--10V. If it reads 12 either the ballast is bypassed or the coil is not drawing current, meaning "some ting wong"

If that is OK, disconnect dist. pickup wire. Again with key "in run" take the dist. connector engine bay end, not the dist end, and repeatedly tap the bare connector pin onto ground. Use a test gap/ spark plug connected to coil tower. You should get one single "snap!" spark each time you ground it

Next, clip your meter to coil+ Crank engine USING THE KEY. You should get "same as battery" during cranking. In other words if battery reads 10.8V during cranking, then the coil+ should be about the same. If it is quite a bit lower or zero, the brown ballast bypass circuit is not working

If that is OK, check spark with test gap at coil tower crank and test using the key. If you get no spark, and the earlier test with the dist. connector did, then you may have a dist. pickup problem OR THE CONNECTOR may not be making contact which is common.

Inspect the inside of the dist. around the pickup / reluctor for rust/ debri, for strike damage, and check dist. shaft for wobble/ looseness. Work the dist connector in /out several times, to scrub the terminals clean, and to "feel" for tightness. Inspect the connector terminals with a lamp to check for corrosion. Same deal with the ECU connector ECU MUST BE GROUNDED
So my meter only reads 8v on coil+ when the engine is cranking. So you said that means the brown ballast bypass circuit is not working. So what should be the next test I should do?
 
Not working or poor connection, but compare it to battery cranking voltage. For all I know, your battery is so dead or old that it is pulling down to 9 when cranking. You might see as much as 1/2--1 volt below battery with that test, but there should really not be "any."

That circuit comes off the ignition switch, through the bulkhead connector, and to the coil+ side of the ballast.

The ignition switch feed is starter relay stud---fuse link---through the bulkhead (big red ammeter wire)---to the ammeter--through the ammeter--out on the big black wire---to the welded splice---branch off to the ignition switch.

So you might have some voltage drop TO the ignition switch, you might have some drop INSIDE the ignition switch, and you might have some drop in the brown wire circuit.

Meanwhile, to see if this is most of or all of the problem, rig yourself a jumper wire direct from the battery (or starter relay stud) to the coil+. Don't leave this connected any longer than you need to test. With this in place, crank the engine and check the spark out of the coil wire with a test gap. You should get a nice snappy spark
 
Wow ! 67Dart273 is the man !! I’m not very good with electrical.... Sounds like 67Dart273 is very schooled in it !!!

One simple thing I would add ! I’ve had problem after problem with a bad distributor rotor ! Not sure why .. But I always carry one with me ! Atleast once a year I have to replace it for a no start condition...... How you can test to see if the rotor is bad.. Is pull the coil wire off the distributor.. Then take the distributor cap off... Hoid the coil wire about an 1/8 inch or so away from the top of the distributor rotor.. Now have someone turn the engine over... If fire jumps from the coil wire to the rotor.. The rotor is bad ! Replace your rotor..
U using Chinese new parts or ???
 
Interesting you brought that up. There HAVE BEEN fake MSD counterfeit modules. If memory serves, they all had the same serial number

Counterfeit MSD 6AL boxes

Counterfeit MSD 6AL Ignitions | Consumer Alert

Counterfeit Product Alert: How To Identify A Real MSD 6AL Ignition VS A Fake - BangShift.com
Yes u are correct and I have noticed very poor quality buttons and boxes for sale the last 5 years !!!
I been horting up all the US stuff I can find to serve me and whoever I pass my stuff on to one day !!!
I have a nice US made collection of boxes and points to serve all my applications if u are ever out and find old engines and can obtain caps and buttons alot of times its older Made in USA stadard ignition products which sadly are made in China now.
 
An inline spark tester is $5 at Harbor Freight. Insert it in a plug wire to verify you are getting spark (neon lamp flashes). You can disconnect the HV wire from the coil and place it near bare metal on the engine or car body. A good electronic ignition should be able to throw a strong spark 1" in the air. See youtubes. Not so far at the ~150 psig in the cylinder. To assure it isn't a fuel problem, disable the fuel supply (so not rich) and see if it runs on starter fluid sprayed down the carburetor throat. The ether has a very wide flammability range so you don't have to spray shots precisely to keep the engine running.
 
Not working or poor connection, but compare it to battery cranking voltage. For all I know, your battery is so dead or old that it is pulling down to 9 when cranking. You might see as much as 1/2--1 volt below battery with that test, but there should really not be "any."

That circuit comes off the ignition switch, through the bulkhead connector, and to the coil+ side of the ballast.

The ignition switch feed is starter relay stud---fuse link---through the bulkhead (big red ammeter wire)---to the ammeter--through the ammeter--out on the big black wire---to the welded splice---branch off to the ignition switch.

So you might have some voltage drop TO the ignition switch, you might have some drop INSIDE the ignition switch, and you might have some drop in the brown wire circuit.

Meanwhile, to see if this is most of or all of the problem, rig yourself a jumper wire direct from the battery (or starter relay stud) to the coil+. Don't leave this connected any longer than you need to test. With this in place, crank the engine and check the spark out of the coil wire with a test gap. You should get a nice snappy spark
I completed the jumper wire from the starter relay stud to the coil+, same result. Tried to fire but won't start. Did some more testing with my volt meter and found that the starter relay stud reads battery voltage/11.9v until I start/crank then it drops to 8.5v. So I thought the starter relay was bad. Bought a new on and same thing. Relay stud reads 11.9v until I start/crank engine and it drops to 8.5v. What would cause this? What test should I do next?
 
That sounds like the battery is dead or one or more of your battery cables/ connections is bad.

You have to learn to test as if you are driving down the road.

Let's say your battery cable goes from battery post----to battery clamp---to cable----to starter relay---to battery.

Maybe it DOESN'T let's SAY it does.

You have a ROAD there. A ROAD MAP.

Measure by stabbing RIGHT INTO the tops of the two battery POSTS. What do you have? If it's much below 12, either the battery is discharged or defective. Charge it up

"Rig" a way to crank the engine either with remote starter button, or screwdriver to jumper the starter relay Another "rig" is to turn on headlights. Either of these will LOAD the battery to PULL IT DOWN and create CURRENT FLOW through the wiring which will show up weak spots

Back up to your road map. First make sure the GROUND CABLE is OK. Put your meter into a low voltage scale. CLIP one lead to the engine block. STAB the remaining probe into the top of the NEG battery post. Now jumper the starter relay. What do you read? Should be VERY low, maybe a few tenths of 1 volt. Anything over .2--.3 is of concern. If so, CLEAN the battery clamps and terminals and try again.

Now Let's start down the ROAD MAP we laid out earlier

Let's say your battery cable goes from battery post----to battery clamp---to cable----to starter relay---to battery.

For now, leave your meter clipped to some point on the engine block. Stab your probe into the top of the POS cable. jumper the starter and read the meter WHILE THE STARTER is cranking. If it is below 10V charge the battery. If the battery won't "come up" take it somewhere and test it. Maybe it's defective/ worn out/ old

Now, with that reading, proceed "down the road." Move the probe to the starter relay. "Let's say" you read 11.3V when stabbed into the top of the battery post, when cranking. "Let's say" you read 8V at the starter relay.

WHAT DOES THAT TELL US?

There is a HUGE voltage drop there. Start by cleaning the battery post and clamp, and re-measure. Backtrack with your probe. If the voltage is OK (near 11.5) at the battery clamp, but low at the starter relay, then the CABLE HAS corroded internally and is bad.

It is simple You simple chase the voltage readings "down the road" that is the wiring PATH

If fact I often call it "the path." "The path" the circuit follows.
 
That sounds like the battery is dead or one or more of your battery cables/ connections is bad.

You have to learn to test as if you are driving down the road.

Let's say your battery cable goes from battery post----to battery clamp---to cable----to starter relay---to battery.

Maybe it DOESN'T let's SAY it does.

You have a ROAD there. A ROAD MAP.

Measure by stabbing RIGHT INTO the tops of the two battery POSTS. What do you have? If it's much below 12, either the battery is discharged or defective. Charge it up

"Rig" a way to crank the engine either with remote starter button, or screwdriver to jumper the starter relay Another "rig" is to turn on headlights. Either of these will LOAD the battery to PULL IT DOWN and create CURRENT FLOW through the wiring which will show up weak spots

Back up to your road map. First make sure the GROUND CABLE is OK. Put your meter into a low voltage scale. CLIP one lead to the engine block. STAB the remaining probe into the top of the NEG battery post. Now jumper the starter relay. What do you read? Should be VERY low, maybe a few tenths of 1 volt. Anything over .2--.3 is of concern. If so, CLEAN the battery clamps and terminals and try again.

Now Let's start down the ROAD MAP we laid out earlier

Let's say your battery cable goes from battery post----to battery clamp---to cable----to starter relay---to battery.

For now, leave your meter clipped to some point on the engine block. Stab your probe into the top of the POS cable. jumper the starter and read the meter WHILE THE STARTER is cranking. If it is below 10V charge the battery. If the battery won't "come up" take it somewhere and test it. Maybe it's defective/ worn out/ old

Now, with that reading, proceed "down the road." Move the probe to the starter relay. "Let's say" you read 11.3V when stabbed into the top of the battery post, when cranking. "Let's say" you read 8V at the starter relay.

WHAT DOES THAT TELL US?

There is a HUGE voltage drop there. Start by cleaning the battery post and clamp, and re-measure. Backtrack with your probe. If the voltage is OK (near 11.5) at the battery clamp, but low at the starter relay, then the CABLE HAS corroded internally and is bad.

It is simple You simple chase the voltage readings "down the road" that is the wiring PATH

If fact I often call it "the path." "The path" the circuit follows.
Starting at the battery itself I get 10.8v when cranking. I followed this (red wire) all the way to the ignition switch which also reads 10.8v when cranking. Then I went to the brown wire on the ignition switch which read 9v when cranking. Which is the same reading I am getting at the coil + when cranking 9v. Could this mean my ignition switch needs to be replaced? Also I pulled a spark plug out and grounded it. When cranking the spark plug is firing but it looks like a yellow spark. My understanding is that means a weak spark right? It should be Blue? Also just FYI I have a new ecu unit highrev 7,500, new ballast resistor 1.2ohms, new coil accel superstock coil, new starter relay, and the battery is only a couple of months old. Thanks I appreciate all of the knowledge.
 
You're on the right track it sounds like

You have to "follow" the voltage through each terminal/ connector/ switch. The fact that you are using a hotter coil may be drawing more current than the stocker and causing further drop. CURRENT is what causes voltage drop through the RESISTANCE of the circuit. The resistance is ADDITAVE. Each terminal, each switch contact, each somewhat corroded wire crimp adds resistance and drop under load

Just follow the path. Man power goes to the IGNITION SWITCH CONNECTOR---through the CONNECTOR--through the SWITCH---back out the CONNECTOR and through the CONNECTOR--to the BULKHEAD CONNECTOR and through the BULKHEAD CONNECTOR and out to the harness and COIL

Each WORD is a place for drop. Think about the bulkhead connector. You have the brown IGN2 CRIMPED to the TERMINAL which mates with the enginge bay side TERMINAL, and that TERMINAL is CRIMPED to the brown wire in the engine bay. The wire then goes to the BALLEST CONNECTOR and is CRIMPED where it joins and continues to the COIL+ TERMINAL and is CRIMPED

Every single point there is a place where drop can occur.

You put the circuit under load (operating) and you check from the "high" (battery end) to the "low" (load end) and look for drop. Sometimes when you find "the big cause" it is WARM. or HOT. And there it is
 
Voltages sound about right.
YW spark is a weak spark, no good.
If the coil you are using needs a ballast res, the res needs to be matched to the coil, not the car. 1.2 ohms sounds high to me, but without knowing the specs, only guessing.
 
Voltages sound about right.
YW spark is a weak spark, no good.
If the coil you are using needs a ballast res, the res needs to be matched to the coil, not the car. 1.2 ohms sounds high to me, but without knowing the specs, only guessing.
So 9volts coming out of the ignition switch and 9v at the coil + is within normal limits?
 
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